Thermally-actuated electric switch



Nov. 23 1926.

1,607,800 E. a. NICHOLSON THERNALLY ACTUATED ELECTRIC SWITCH 2Sheis-Shaot 1 Filed A ril 12. 1926 N0v. "-3 1926. v

, 1,607,800 E. G. NICHOLSON THERMALLY ACTUATED ELECTRIC SWITCH FiledApril 12, 1926 2 Sheets-Sheet 2 Patented Nov. 23, lQf Zfi.

irorsoa EDWARD GEORGE nrcii'otsonor HORSELL, woxrne, ENGLAND.

THERMALLY-ACT'UATED ELECTRIC SWITCH.

Application filed April 12, 1926, Serial No. 101,524., and in GreatBritain Apri1 29, 1925.

This invention relates to thermally actuated switches particularlyintended to be used for preventing overheating of electric heatingapparatus, of the kind in wh1ch spring mechanism tending to open theswitch is normally held out of operation by fusible alloy or solderwhich melts or softens when a certain predetermined temperature isreached.

By way of example two embodiments of the invention are illustrated inthe accompanying drawings, in which- Figure 1 is a plan view from belowof the first embodiment.

Figure 2 is a side view in section of Figure 1.

Figure 3 is an end view, half in section on the line II of Figure 1.

Figure 1 is a plan view from below of the second embodiment.

Figure 5 is a side view in section of Figure 4, and

Figure 6 is an end view in section on the line IIII of Figure 4.

Referring first to Figures 1 to 3, a heating element in two sections 1and 2 is mounted on the true bottom 3 of a heating appliance and may beenclosed, together with the switch, by a false bottom (not shown). Thesections 1, 2, are respectively connected to one of the supply plugs 45, and are provided at their opposite ends with connecting contacts 6,7. The circuit is normallycompleted by a bridging spring 8 which 15 secured to a frame 9 having a tooth 10 engaging a ratchet wheel 11normally secured on to its spindle 12 by a suitable fusible solder oralloy. The spindle is mounted in close contact with the bottom 3 so thatit attains as nearly as possible the same temperature as the appliance.The frame 9 may be conveniently guided by making the contact 7 longer ormore extended than the contact 6, as shown in Figure 1. This tends totilt the frame so as to keep the tooth 10 in engagement with the wheel11. A. pin 13 provided with a setting button 14 operable from theoutside of the appliance is fastened to the frame 9 and a spring 15 actsto move the spring 8 out of engagement with the contacts 6, 7 If thetemperature of the appliance rises beyond a predetermined limit thesolder or alloy melts, thus allowing the ratchet wheel 11 to rotate andthe spring 15 therefore draws the spring 8 out of engagement with thecontacts 6, 7 thus breaking the circuit. part of the frame 9 adjacent tothe tooth 10 causes the tooth to come entirely out of engagement with.the wheel after it has moved a short distance and before the circuit isopened. This ensures a clean and rapid break of the circuit in spite ofany sluggishness in rotation of the wheel, and allows the ratchet wheelto stop rotating as soon as possible. ture has fallen sufiicient-ly thesolder or alloy sets and secures the wheel and the switch can be re-setby pressing the button 14. If desired the resetting button let may beenclosed within the switch chamber.

Referring now to Figures 4 to 6 the switch comprises a rotating switchbar 16 which bridge-s a pair of contacts 17, 18. The ratchet wheel 19 isformed on a sleeve 20 soldered to the fixed spindle 25. This sleeve 20forms a journal for the bar 16 which carries a awl 26 in engagement withthe ratchet w eel. A spring 21 operates the switch. In order to ensure arapid break despite sluggish action of the ratchet wheel a cam 22 issecured on the spindle 25 and the pawl is broadened to ride on the camwhich lifts the pawl out of engagement with the ratchet wheel after thebar has moved a short distance but. before it has left the contacts. Theswitch may be reset by a spring button and connecting link or push rod(not shown) arranged to be operable from outside or not as desired.

The ratchet member may be provided with a spring back stop of the usualkind in order to ensure that it always stops with the teeth in a certaindefinite position so that the switch when reset always takes the sameposition. This is not essential, however, since the range of engagementof the switch blade with the contacts will cover any variation in thestopping position of the ratchet member. Finally, more than one switchblade and more than two contacts may be used where desired, and theswitch may if desired be mounted in a separate chamber from the heatingelement.

What I claim is 1. In a thermally actuated switch of the kind set forth,a ratchet member normally held by a fusible alloy, a spring actuatedpart, a pawl on said spring actuated part coacting with said ratchetmember, and a guide member co-operating with said ratchet member forpositively raising said pawl out The straightv edge of the As soon asthe temperaill) of engagement with said ratchet member forming a breakin the heater circuit positioned so as to tilt the frame so that itssaid tangential edge contacts with, and its pawl engages, said ratchetmember, when said Contact bridge bears on said contacts to complete thecircuit, a resetting bar on said frame extending outside the appliance,and spring means. tending to movesaid bridge out of contact with saidcontacts.

Intestimony whereof I have signedmy name to this specification.

EDWARD GEORGE NICHOLSON.

